[werk_ag]

One thing I don't understand: Why do you want to "correct" for humidity?

Hi,

I don't properly want! The reason is the same why all dust measurements must be corrected in relation with humidity. That main reason why all dust sensors include a Temperature / Humidity sensor, is because we need the humidity reading to apply a correction on the raw readings.
All your dust sensors (no matter the brand), apply corrections to the raw readings from the dust sensor.

No going in to much details (also, I'm not the best one to do it), high grade CO2 measurement equipments, are very complex units. The fresh air before entering the measurement chamber is humidified or dehumidified until reach 50%RH, otherwise the readings may not reflect a real increase or decrease of CO2 in the air (as we humbly tried to demonstrate).

At fresh air, far from a source emitting CO2, the readings should always be always around 400ppm. Just the error margin of the sensors (+-30ppm Sensirion, +-50ppm MH-Z19) we are talking about, is enough to understand that they aren't suitable for serious measurement of CO2 in the atmosphere. However, the same way as dust sensors are playing an important role in bringing people attention to Air Quality, the CO2 sensors may also have a part on that role. Get people's attention to environmental questions is the main goal.

Happily, our small team can count with someone with a great knowledge on this matters, including weather, and we all had learned a lot from him.
Much before the appearing of the Purple Air and other popular dust sensors, we were already investigating and working on this field, using not well know dust sensors from Sharp (very hard to read and somewhat expensive). The same is happening now regarding outdoor CO2 measurements, we are trying to figure the maths that eventually may allow us to use inexpensive sensors, and get reliable measurements.
Connecting a sensor to a microcontroller and get a number from it, is a quite easy task, the hard part is the other things, like the maths involved when correction of the readings is needed.


The publication of this topic, regarding CO2 measurement, was more or less like launching a theme for reflection.
If at least one person is going to investigate about this matter, it has already been worth it. And I bet you will!

Rgs